Hello,
Regarding to adding {STARTPOLICYLINK} and {ENDPOLICYLINK}.
This won't work, because the policy link is not actually "linking" to a policy but triggering a JavaScript function to show it.
Also, as far as I know, the data policy agreement has to be accepted before the survey starts.
The policy link placeholders will not actually help you achieve that.

But I back your question for the data policy text to be available as a variable in the survey, even though we strongly recommend showing the data policy notice at the beginning of the survey to be GDPR safe.
Any showing in the survey can only be additional to that.